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 <h1>COMPONENT PROPERTY SYNTAX</h1><br>
 <p>
  Component property strings can be set in the usual way with the <kbd>'q'</kbd> on a selected
  component instance or by menu <kbd>Properties&nbsp;--&gt;&nbsp;Edit</kbd>
 </p> 
 <img src="component_properties.png">
 <p>
  The dialog box allows to change the property string as well as the symbol reference. The property string
  is essentially a list of <kbd>attribute=value</kbd> items. As with symbol properties if a <kbd>value</kbd>
  has white space it should be double-quoted.
  The following property definitions are identical:
 </p>
 <pre class=code>
name=mchanged_name model=nmos w=20u l=3u m=10
 </pre><br>
 <pre class=code>
name="mchanged_name" model="nmos" w="20u" l="3u" m="10"
 </pre><br>
 <p> 
  Given the role of the <kbd>"</kbd> character, if quoted values are needed escapes must be used, like in 
  the following example where the model name will be with quotes in netlist:
 </p>
 <pre class=code>
name="mchanged_name" model="\"nmos\"" w="20u" l="3u" m="10"
 </pre>
 <p>or</p>
 <pre class=code>
name="mchanged_name" model=\"nmos\" w="20u" l="3u" m="10"
 </pre>
 <p>
  the resulting SPICE netlist will be:<br>
  <kbd>mchanged_name DRAIN GATE SOURCE BODY "nmos" w=20u l=3u m=10</kbd>
 </p>
 <p> 
  There is no limit on the number of <kbd>attribute=value</kbd> items, each attribute should have a corresponding 
  <kbd>@attribute</kbd> in the symbol definition format, but this is not a requirement. There are a number
  of special attributes as we will see later.
 </p>
 <p class="important"> 
  Important: a <kbd>name=&lt;inst_name&gt;</kbd> item is mandatory and must be placed  
  in component property string to get a valid netlist, as this is the partname or so-called refdes (reference designator).
  If <kbd>&lt;inst_name&gt;</kbd> is already used in another component XSCHEM will
  auto-rename it to a unique name preserving the first letter (which ts a device type indicator
  for SPICE like netlists).
 </p>
 <h3>PREDEFINED COMPONENT ATTRIBUTES</h3>
 <ul>
  <li><kbd>name</kbd></li>
  <p> This defines the name of the instance. 
    Names are unique, so if for example multiple MOS components are
    placed in the design one should be named <kbd>m1</kbd> and the second <kbd>m2</kbd> or anything 
    else, provided the names are different. XSCHEM enforces this, 
    unless <kbd>Options -&gt; allow duplicated instance names</kbd> is set. If a name is given that already
    exist in the current schematic it will be renamed. Normally the template string defines a default
    name for a given component, and expecially for SPICE compatibility, the first character must NOT 
    be changed. For example, the default name for a MOS transistor is <kbd>m1</kbd>, it can be renamed
    for example to <kbd>mcurr_source</kbd> but not for example to <kbd>dcurr_source</kbd>. XSCHEM 
    does not enforce that the first character is preserved, it's up to the designer to keep it 
    consistent with the component type.</p>
  <li><kbd>embed</kbd></li>
  <p>
   When the <kbd>embed=true</kbd> is set on a component instance
   the corresponding symbol will be saved into the schematic (.sch) file on the next save operation.
   This allows to distribute schematic files that contain the used symbols so these
   will not depend on external library symbols.
   When this attribute is set on a component instance, all instances in the schematic referring to the same 
   symbol will use the embedded symbol definition.
   When descending into an embedded symbol, any changes will be local, meaning that no library symbol
   will be affected. The changes will be saved using the embedded tag (<kbd>[...]</kbd>) into the
   schematic file.
   Removing this attribute will revert to external symbols after saving and reloading the schematic file.

  </p>
  <li><kbd>url</kbd></li>
  <p> This attribute defines a location (web page, file) that can be viewed when hitting the
    <kbd>&lt;shift&gt;H</kbd> key (or <kbd>&lt;Alt&gt; left mouse buttoni</kbd>) on a selected component. 
    This is very useful to link a datasheet to a
    component, for example. The default program used to open the url is <kbd>xdg-open</kbd>. 
    this can be changed in the <kbd>~/xschemrc</kbd> configuration file with the <kbd>launcher_default_program</kbd>
    variable.
    <kbd>url</kbd> can be an http link or a local file that has a default association known to xdg-open.</p>
  <li><kbd>program</kbd></li>
  <p> this attribute can be used to specify an application to be used to open the <kbd>url</kbd> link,
      if the default application has to be changed or the file type is unknown.
      for example <kbd>program=evince</kbd> may be given to specify an application for a pdf file
      specified with <kbd>url</kbd></p>
  <li><kbd>tclcommand</kbd></li>
  <p> this can be any tcl statement (or group of statements separated by semicolons) including all xschem-specific
      commands, the statement will be executed when pressing the <kbd>&lt;shift&gt;H</kbd> key 
      (or <kbd>&lt;Alt&gt; left mouse button</kbd>) on the selected instance.
      <br>The <kbd>tclcommand</kbd> and <kbd>url</kbd> properties are mutually exclusive.</p>
  <img src="component_properties3.png">
  <li><kbd>only_toplevel</kbd></li>
  <p>this attribute is valid only on <kbd>netlist_commands</kbd> type symbols and specifies that the 
    symbol should be netlisted only if it is instantiated in the top-most hierarchy. This is very usefull
    for spice commands. Spice commands are placed in a special <kbd>netlist</kbd> component as we will see
    and are meaningfull only when simulating the block, but should be skipped if the component
    is simulated as part of a bigger system which has its own (at higher hierarchy level)
    <kbd>netlist</kbd>component for Spice commands.</p>
  <img src="component_properties0.png">
  <li><kbd>lock</kbd></li>
  <p> A <kbd>lock=true</kbd> attribute will make the symbol not editable. the only way to make it editable again is 
      to right click on it to bring up the edit attributes dialog box and set to false. This is useful for title
      symbols. </p>
  <li><kbd>highlight</kbd></li>
  <p>If set to <kbd>true</kbd> the symbol will be highlighted when one of the nets attached to its pins are highlighted.</p>
  <li><kbd>net_name</kbd></li>
  <p>If set to <kbd>true</kbd> the <kbd>#n:net_name</kbd> symbol attributes will display the net names attached to pin terminals.
     the <kbd>n</kbd> is a pin number or name.</p>
  <li><kbd>place</kbd></li>
  <p> This 
    <kbd>place=end</kbd> attribute is only valid only for <kbd>netlist_commands</kbd> type symbols, and tells
    XSCHEM that this component must be netlisted last. This is necessary for some spice commands 
    that need to be placed <b>after</b> the rest of the netlist.</p>
  <li><kbd>spice_ignore</kbd></li>
  <p> This tells XSCHEM that for SPICE netlist this component will be <b>completely</b> ignored.</p>
  <li><kbd>verilog_ignore</kbd></li>
  <p> This tells XSCHEM that for Verilog netlist this component will be <b>completely</b> ignored.</p>
  <li><kbd>vhdl_ignore</kbd></li>
  <p> This tells XSCHEM that for VHDL netlist this component will be <b>completely</b> ignored.</p>
  <li><kbd>sig_type</kbd></li>
  <p> For VHDL type netlist, this tells that the current label names a signal (or constant) of
    type <kbd>sig_type</kbd>. For example a label can be placed with name <kbd>TEST</kbd> and 
    <kbd>sig_type=BIT</kbd>. The default type for VHDL if this property is missing  is <kbd>std_logic</kbd>.
    The following picture shows the usage of <kbd>sig_type</kbd> and the resulting VHDL netlist.
    This property is applicable only to <kbd>label</kbd> type components: <kbd>ipin.sym</kbd>, 
    <kbd>iopin.sym</kbd>, <kbd>opin.sym</kbd>, <kbd>lab_pin.sym</kbd>, <kbd>lab_wire.sym</kbd>.
  </p>
  <img src="component_properties1.png">
  <li><kbd>verilog_type</kbd></li>
  <p>This is the same as sig_type but for verilog netlisting: can be used to declare a <kbd>wire</kbd>
     or a <kbd>reg</kbd> or any other datatype supported by the verilog language.
  </p>
  <li><kbd>generic_type</kbd></li>
  <p><kbd>generic_type</kbd> defines the type of parameters passed to VHDL components.
    Consider the following examples of placement of <kbd>generic_pin</kbd> components in a 
    VHDL design: 
  </p>
  <img src="component_properties2.png">
  <p> As you will see in the <a href="parameters.html">parameters</a> slide, generics (they are just
    parameters passed to components) can be passed also via property strings in addition to using 
    <kbd>generic_pin</kbd> components.</p>
   
  <li><kbd>class</kbd></li>
  <p>The <kbd>class</kbd> attribute is used to declare the class of a VHDL signal, most used classes are
    <kbd>signal</kbd> and <kbd>constant</kbd>. Default if missing is <kbd>signal</kbd>.</p>
  <li><kbd>device_model</kbd></li>
  <p>
   This attribute contains a SPICE .model or .subckt specification (<kbd>device_model=".model D1N4148 D ...."</kbd>)
   that will be printed at end of netlist only once for the specified component (D1N4148 in the example).
   <kbd>device_model</kbd> attributes defined at instance level override the <kbd>device_model</kbd> set
   in the symbol if any.
  </p>

  <li><kbd>pinnumber(name)</kbd></li>
  <p> This will override at instance level the value of attribute <kbd>pinnumber</kbd> of pin <kbd>name</kbd> of the symbol.
      This is mainly used for tedax, where by back annotation a connection to a symbol must be changed.</p>
  <li><kbd>pinnumber(index)</kbd></li>
  <p> This will override at instance level the value of attribute <kbd>pinnumber</kbd> of <kbd>index</kbd>th pin of the symbol.
      This is mainly used for tedax, where by back annotation a connection to a symbol must be changed.
      This notation is faster since xschem does not have to find a pin by string matching.</p>
 </ul><br>
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